1. Field of the Invention
The present invention relates to a plate assembly that supports a workpiece in a processing chamber while the workpiece is processed in a vacuum. More specifically, the present invention relates to apparatus for processing a semiconductor wafer in a high vacuum atmosphere, and to a plate assembly for supporting the wafer in the processing chamber of such an apparatus.
2. Description of the Related Art
Currently, due to the widespread use of computers, semiconductor memory devices are being rapidly developed to provide greater memory storage and faster operating speeds. To this end, current processing technology in the art of manufacturing semiconductor devices is focused on developing and realizing memory devices having a high degree of integration, response speed, and reliability. These technologies include thin film forming, fine pattern forming, and ion-implantation processes.
Furthermore, the conditions of pressure, temperature, and gas flow must be accurately controlled during these semiconductor device manufacturing processes. If the processing conditions are not accurately controlled, the resulting semiconductor devices may fail or produce process errors. That is, the ability to accurately control the processing conditions during the manufacturing of semiconductor devices has a direct affect on the reliability of the devices and the productivity of the manufacturing process
In particular, recent semiconductor device manufacturing processes rely on the creation of a stable high vacuum condition. For example, current ion-implantation processes may be carried out in a vacuum of 1.0xc3x9710xe2x88x926 to 1.0xc3x9710xe2x88x927 Torr.
Furthermore, a semiconductor device is manufactured by repeatedly carrying out the thin film forming process, the fine pattern forming process, the ion-implantation process and the like. In the manufacturing of semiconductor device, therefore, a wafer must be accurately positioned throughout the course of its being transported and processed several times.
As can be seen from the description above, the manufacturing of a semiconductor device requires not only controlling the processing conditions (vacuum, temperature and gas flow), but also the position of the wafer, the processing order, and the like. For example, an ion-implantation process must be carried out as follows. A vacuum of 1.0xc3x9710xe2x88x926 Torr, for example, must be established in a processing chamber. The wafer is placed on a plate, i.e., a chuck, in the processing chamber. In particular, the wafer is set on a predetermined portion of the plate. As mentioned above, a high degree of vacuum is established in the processing chamber. Therefore, members are disposed on the plate to position the wafer as the wafer is set on the plate.
Korean Patent Laid-Open Publication No. 1999-6995, Korean Patent Laid-Open Publication No. 2000-34535, Japanese Patent Laid-Open Publication No Heya 7-221042 and U.S. Pat. No. 4,971,676 issued to Doue et al. all disclose examples of a wafer support plate having positioning members disposed thereon.
Now, an example of the way in which a wafer is set on a wafer support plate in a high vacuum atmosphere in a processing chamber will be described with reference to FIGS. 1 and 2.
FIG. 1 is a schematic diagram of an apparatus for implanting ions into a wafer W. The apparatus includes a processing chamber 10 and a plate assembly 12 disposed in the processing chamber 10. The plate assembly 12 has a pad 12a whose surface contacts the rear surface of the wafer W when the wafer W is positioned on the plate assembly 12, and a plate 12b supporting the pad 12a. The plate assembly 12 may also include a fence 20 as a stop for the wafer W, and a flange 22 that guides the wafer W during the movement of the wafer W onto the pad 12a. The fence 20 and the flange 22 extend along half the periphery of the pad 12a. The apparatus for implanting ions in the wafer W also includes a robot arm 14. The robot arm 14 is used to transport the wafer W from outside the processing chamber 10 onto the plate assembly 12 and from the plate assembly 12 to the outside of the processing chamber 10. Furthermore, the apparatus includes a lifter 18 having lifter pins 16. The lifter 18 and the lifter pins 16 support the rear surface of the wafer to position and/or lift the wafer on/from the plate assembly 12.
Referring now to FIG. 2, the wafer W is moved by the robot arm 14 onto/from the plate assembly 12. More specifically, the lifter 18 and the lifter pins 16 are raised. At this time, the robot arm 14 is positioned between the plate assembly 12 and the wafer W which is resting on the lifter pins 16. Then, the lifter 18 is lowered. Accordingly, the wafer W is placed on the robot arm 14, and is in turn transported by the robot arm 14.
At this time, the wafer W is positioned on the robot arm 14 by members (not shown) disposed on the plate assembly 12. If the wafer W is not positioned precisely on the robot arm 14, the wafer W may be damaged, for example, scratched, by the robot arm 14 In an extreme case, the mis-positioned wafer W may be dropped while being carried by the robot arm 14. Specifically, in many instances, the wafer W may not settle precisely on the robot arm 14 despite the presence of the wafer-positioning members of the plate assembly 12. The reason for this is that a pressure difference may be present or suddenly created in the space between the plate assembly 12 and the wafer W at the time the wafer W is being raised by the lifter 18 and the lifer pins 16. The pressure difference is created by a vacuum of 1.0xc3x9710xe2x88x928 Torr, for example, produced in the processing chamber 10.
When the surface of the wafer W is scratched or when the wafer W has fallen from the robot arm 14 for the reasons described above, the damaged wafer must be reworked or discarded. Therefore, the use of the prior art apparatus lowers the productivity of the semiconductor device manufacturing process.
An object of the present invention is to solve the above-described problem of the prior art.
More specifically, one object of the present invention to provide a plate assembly that will allow a vacuum atmosphere in a processing chamber to act on the rear surface of a workpiece supported by the plate assembly.
It is likewise another object of the present to provide an apparatus for processing a workpiece in a vacuum wherein a minimal pressure difference is produced at both sides of the workpiece while the workpiece is being supported. thereby minimizing the tendency of the workpiece to be mis-positioned when it is raised off of the support
The plate assembly includes an underlying plate and a pad having a plurality of recesses in the upper surface thereof. Preferably, the recesses are parallel grooves that extend straight across the upper surface from one side thereof to the other. Furthermore, the plate assembly is generally disc-shaped and has a larger area than that of the workpiece so that the entire rear surface of the workpiece is situated on the pad.
The plate assembly is disposed in a processing chamber in which a process is carried out on the workpiece under a vacuum. The workpiece is supported on the pad of the plate assembly One or more lift pins are provided to lower the workpiece onto the plate assembly or raise the workpiece up off of the plate assembly. A robot arm can moved into position to receive the workpiece from the lifter pin(s) or transfer the workpiece to the lifter pin(s). Preferably, the robot arm has a bifurcated (Y-shaped) free end so as not to interfere with the operation of the lifter pin(s). Also, the robot arm has a working range that allows it to transfer the wafer from the vicinity of the plate assembly to the outside of the processing chamber and vice versa.
The workpiece may be a wafer used in the manufacturing of semiconductor devices. In this case, the processing apparatus may be an apparatus for forming a film on the wafer, an apparatus for forming a pattern on the wafer or an apparatus for implanting ions into the wafer.
In the processing apparatus, the wafer is placed on the plate assembly and is processed. After the workpiece is processed, the lift pin(s) is/are raised into contact with the rear surface of the workpiece to transfer the workpiece off of the pad of the plate assembly. At this time, the recesses in the upper surface of the pad of the plate assembly allow the vacuum atmosphere in the processing chamber to act at the rear surface of the workpiece. Because the pressure is significantly equalized at both sides of the wafer, the workpiece is not disturbed as it is raised by the lift pin(s). As a result, the wafer will not be scratched by the robot arm and thus, the wafer can be safely transported.